RFR: 8264851: Shenandoah: Rework control loop mechanics to use timed waits [v2]

[William Kemper]

> We use a similar mechanism in `shGenerationalControlThread` already. Using a timed wait allows the control thread to be woken up before the wait expires.

William Kemper has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains three additional commits since the last revision:

 - Merge remote-tracking branch 'jdk/master' into use-timed-wait-for-control-thread
 - Add documentation and make new method private
 - Use timed wait/notify for more timely control thread reactions

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Changes:
  - all: https://git.openjdk.org/jdk/pull/27502/files
  - new: https://git.openjdk.org/jdk/pull/27502/files/73c1849a..fd47d57f

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=27502&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=27502&range=00-01

  Stats: 22555 lines in 759 files changed: 13114 ins; 5271 del; 4170 mod
  Patch: https://git.openjdk.org/jdk/pull/27502.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27502/head:pull/27502

PR: https://git.openjdk.org/jdk/pull/27502